Transport Systems
Transport systems are responsible for moving substances (gases, nutrients, waste products,
etc.) throughout an organism.
1. Types of Transport:
○ Active Transport: Requires energy (ATP) to move substances against their
concentration gradient (from low to high concentration).
○ Passive Transport: No energy is required; substances move down their
concentration gradient (from high to low concentration). Examples include
diffusion and osmosis.
2. Circulatory System (Humans):
○ The circulatory system is responsible for transporting oxygen, nutrients,
hormones, and waste products.
○ Components: Blood, heart, blood vessels (arteries, veins, capillaries).
○ Heart: A muscular organ that pumps blood throughout the body. The human
heart has four chambers (two atria and two ventricles).
○ Blood Vessels:
■ Arteries: Carry oxygenated blood away from the heart.
■ Veins: Carry deoxygenated blood back to the heart.
■ Capillaries: Small blood vessels where gas exchange occurs.
Lungs and Gas Exchange
The lungs are part of the respiratory system, where gas exchange (oxygen and carbon dioxide)
occurs.
1. Structure of the Lungs:
○ Trachea: A tube that carries air to the lungs. It branches into the bronchi.
○ Bronchi and Bronchioles: The bronchi branch into smaller tubes called
bronchioles, which lead to the alveoli.
○ Alveoli: Tiny air sacs in the lungs where gas exchange takes place. The walls of
alveoli are one cell thick for efficient gas exchange.
2. Gas Exchange Process:
○ Oxygen from the air diffuses across the alveolar membrane into the bloodstream.
○ Carbon dioxide (a waste product) diffuses from the blood into the alveoli and is
exhaled.
3. Efficiency of Gas Exchange:
○ The large surface area of the alveoli and their thin walls allow for efficient
diffusion of gases.
○ The vast network of capillaries surrounding the alveoli also ensures effective gas
exchange.
Gut Structure and Function
The digestive system breaks down food, absorbs nutrients, and eliminates waste.
1. Key Parts of the Digestive System:
○ Mouth: Food is mechanically broken down by chewing and chemically broken
down by enzymes in saliva.
○ Esophagus: A muscular tube that moves food from the mouth to the stomach.
○ Stomach: A muscular organ that secretes acids and enzymes to break down
food.
○ Small Intestine: The primary site for digestion and nutrient absorption. It is lined
with villi, which increase surface area for absorption.
○ Large Intestine: Absorbs water and forms solid waste (feces).
○ Rectum and Anus: Where solid waste is stored and eliminated.
2. Villi and Microvilli:
○ Villi are finger-like projections in the lining of the small intestine that increase
surface area for nutrient absorption.
○ Microvilli are even smaller projections on the surface of epithelial cells on villi,
further increasing the surface area for absorption.
Surface Area-to-Volume Ratio
The surface area-to-volume ratio is a critical factor for the efficiency of transport processes in
cells and organisms.
1. Importance in Cells:
○ As a cell grows, its volume increases faster than its surface area. This limits the
cell's ability to exchange substances efficiently.
○ Small Cells: Have a higher surface area relative to their volume, making them
more efficient at exchanging materials with their surroundings.
○ Large Organisms: Need specialized transport systems (like circulatory systems)
to transport materials efficiently across their bodies.
2. Adaptations for Increased Surface Area:
○ Alveoli in the lungs have a large surface area for efficient gas exchange.
○ Villi in the small intestine increase the surface area for nutrient absorption.
○ Root Hairs in plants increase the surface area for water and nutrient absorption.
Key Terms:
● Diffusion: The movement of particles from an area of high concentration to an area of
low concentration.
● Osmosis: The movement of water across a selectively permeable membrane from an
area of low solute concentration to an area of high solute concentration.
● Enzyme: A protein that catalyzes biochemical reactions, speeding them up.
● Peristalsis: The wave-like muscle contractions that move food along the digestive tract.
● Capillaries: Tiny blood vessels where the exchange of gases, nutrients, and waste
occurs.
